Exhaust gases from combustion processes often carry substantial amount of solid and gaseous contaminants which must be removed before the gases are vented to the atmosphere. This problem is especially severe in the case of incinerators burning municipal trash and garbage. In addition to the usual solid and gaseous contaminants, incinerator exhaust gas often contains malodorous contaminants which intensify the problem.
It has been proposed to remove particulates from incinerator exhaust gases by means of electrostatic precipitators and indeed electrostatic precipitators have found use in the treatment of a large variety of particulate laden gas streams. Electrostatic precipitators are generally effective to remove particulate matter but cannot remove the usual gaseous contaminants.
A wide variety of wet scrubbers have been proposed, and used, for the removal of particulate matter and odorous components from waste gases. Venturi scrubbers, for example, utilize the energy of the gas stream to impact upon a liquid curtain causing atomization. Collisions between solid particles and liquid droplets tends to remove particulates from the gas and the liquid droplets can also absorb or otherwise react with certain components of the gas stream. While effective, venturi scrubbers require a relatively high pressure drop to function properly and thus are characterized by high operating costs.
It is also well known to treat odorous gases by contact with scrubbing liquids in packed towers of various types. This approach is effective to remove odorous materials but packed towers are inherently subject to fouling and plugging especially when the gas being treated carries particulate matter. Like venturi scrubbers, packed towers generally display a significant pressure drop and require a relatively high energy input to move the gas through the tower.
Yet another approach to the removal of solid particulates and noxious gases from exhaust gas streams is illustrated by U.S. Pat. No. 3,473,298. Exhaust gases are first contacted with a water spray which serves to cool the gases and remove at least the larger particulates. Thereafter, the exhaust gas stream is passed through a condenser which further cools the gas and causes condensation of water vapor. It has been found, however, that conventional tube-type heat exchangers quickly foul and plug in this service especially when treating dirty exhaust gas streams such as those produced by the burning of refuse in incinerators.